The invention relates to an arrangement for controlling a pacemaker in which a control signal corresponding to cardiac volume is generated by an impedance measurement with the aid of electrodes disposed intracardially, which signal is used for influencing the stimulation frequency of the stimulation pulses of the pacemaker.
Different measuring values can be used to control the stimulation frequency of a pacemaker.
On the basis of new realizations, physiological parameters, such as temperature of the venous blood, breathing frequency or other intrathoracic function parameters of the patient, when extensively matched to one another, are preferably used to control the stimulation frequency. Likewise, it is possible to adapt the stimulation frequency of the pacemaker to certain stress situations of the patient using the detection of the stroke volume or cardiac volume.
An arrangement is known from DE-OS 36 29 587 with which the ventricular volume can be determined in connection with an impedance measurement. According to this document, an intracavitary impedance catheter is used. This impedance catheter comprises a tube that is to be inserted intraventicularly and has a plurality of pairs of surface electrodes disposed at a distance from one another. These electrodes are activated by a corresponding number of electrical signals having respectively different frequencies, and serve as a current source or voltage-measuring points. The instantaneous ventricular volume can be calculated from the measured voltage, the magnitude of the impressed current and a few patient-specific, geometrical values. The precision of the method can be increased with an increasing number of electrode pairs. The stroke volume results from the difference between the calculated minimum volume for the end systole and the maximum volume for the end diastole.
The proposed multipole impedance catheter is basically suited for determining the ventricular volume. However, for use in connection with permanently implanted pacemakers, it has the significant disadvantage that the necessary larger number of which are installed parallel to each other and are insulated from one another, is associated with a considerable structural expenditure, if a reliable connection of the corresponding electrodes is to be assured in the bending stresses of the impedance catheter necessitated by the permanent use. A further disadvantage is that the necessary multipole plug connection to the pacemaker leads to a considerable increase in volume. Moreover, in the proposed measuring method, it is not possible to use electrode arrangements that are already implanted for an impedance measurement, so the additional plug connections even further increase the volume of the pacemaker.